Aircon problems D2

**devo** · 15th April 2017, 07:20 PM

Originally Posted by rick130

Not so.

The system can be short of refrigerant and the LP switch may still be in and let the comp start, and if the refrigerant charge is low enough it will trip the LP and cut out at some point after running for a while.
Depending on how short it is the compressor may still run almost continuously, but not necessarily cool, or it may cut out almost instantly.
It all depends on what the LP is set to cut out at, and what the refrigerant charge actually is.

Gauges need to be hooked up to see what's happening otherwise we are guessing

Thanks rick130
That may explain why the air is cool when I first start the engine and gets warmer as the engine reaches running temp. All comes back to gas at the moment.
that is where I started and looks like I got a bad steer.
Cheers.
Will try again with the gas check.

**rick130** · 15th April 2017, 07:25 PM

Originally Posted by sierrafery

That switch works exclusively on system pressure so if the pressure is below the minimum limit it will be open and not let the compressor clutch to engage

Attachment 121928

As does any LP switch on any refrigeration/a-c system.

You can be short of refrigerant and the compressor still run.

FWIW those pressures seem very wrong.
The suction ones are showing the cutout above 0*C, usually it's well below 0* as our normal running pressure will be something like -6* to -10* or so depending on evaporator size, and the discharge pressures are ridiculously high, dangerously so.

Put it this way, 29psi is almost +1*C which would give us a roughly 6-10* evaporator temp (it depends on the actual evap size, I've never had gauges on a D2) and a a higher again air off temp.
I've never seen an LP set that high, and any car/truck/tractor system I've worked on ran well below those pressures normally.

We use adjustable pressure switches on large commercial/industrial stuff, and again they aren't set anywhere near those pressures.
Those HP switching pressures are higher than anything we use with R404a, a refrigerant that runs at substantially higher pressures than R134a.

**sierrafery** · 15th April 2017, 07:47 PM

To rule out a pressure issue remove the grille, unplug the switch and bridge the pins in the plug, switch on aircon to cool and if the compressor kicks in wthis way then check the pressure and if it's OK it means the switch is at fault, if the compressor doesnt kick in with bypassed switch you can troubleshoot further

**scarry** · 15th April 2017, 09:10 PM

Originally Posted by sierrafery

That switch works exclusively on system pressure so if the pressure is below the minimum limit it will be open and not let the compressor clutch to engage

Attachment 121928

That is correct,same as my genuine workshop manual for the D2.

The switch is a dual type mounted in the receiver drier.
There is not a switch on the low side of the system.
Back to the OP's issues,also if the compresser is running but not pumping,the pressure switches will not trip,but it will not cool.

Your saying the air is cool to start off with.If you mean it is cool until the engine warms up,you could have issues with the servo motors that operate the air duct flaps,as the heater matrix has coolant running through it all the time. The supply air temperature is controlled by servo motors moving the relevant blend flaps in the air ducts.If they are not working correctly you may be getting too much heated air,instead of cooled air.

The system could also be low on refrigerant,which is more than likely the issue,the system has to be almost out of refrigerant to trip a pressure switch on the high side of the system at 29psi.

As Rick has said,a set of gauges on the system is the go to check operating pressures,then go from there.

**rick130** · 15th April 2017, 09:18 PM

Originally Posted by scarry

That is correct,same as my genuine workshop manual for the D2.

The switch is a dual type mounted in the receiver drier.
There is not a switch on the low side of the system.
Back to the OP's issues,also if the compresser is running but not pumping,the pressure switches will not trip,but it will not cool.

Your saying the air is cool to start off with.If you mean it is cool until the engine warms up,you could have issues with the servo motors that operate the air duct flaps,as the heater matrix has coolant running through it all the time. The supply air temperature is controlled by servo motors moving the relevant blend flaps in the air ducts.If they are not working correctly you may be getting too much heated air,instead of cooled air.

The system could also be low on refrigerant,which is more than likely the issue.

As Rick has said,a set of gauges on the system is the go to check operating pressures,then go from there.

Are those pressures kosher Paul ?

The HP ones are insane.

Thankfully the new D2 a/c is working fine, and I don't have any tools with me anyway....

**scarry** · 15th April 2017, 09:23 PM

Originally Posted by rick130

Are those pressures kosher Paul ?

The HP ones are insane.

Thankfully the new D2 a/c is working fine, and I don't have any tools with me anyway....

I just edited my post

Yes i know they are insane,and they use the switch for an LP safety as well.

Just imagine having a fault and running at 400psi on 134a,and it doesn't trip anything

**rick130** · 15th April 2017, 09:53 PM

Originally Posted by scarry

I just edited my post

Yes i know they are insane,and they use the switch for an LP safety as well.

Just imagine having a fault and running at 400psi on 134a,and it doesn't trip anything

Ok, that's just plain dumb.

29psi in the high side is pumping air, there's no refrigerant left.

That HP cutout pressure is worse than scary, we set R404 cutouts lower. It's almost 410a territory.
The cutout pressure is 91*C !

**sierrafery** · 15th April 2017, 10:05 PM

It's in the description of that dual pressure switch that it's there to protect the system from extremes of presures in case something goes wrong, it's not used for cooling management cos that's achieved based on the evaporator outlet air temp sensor and the ECU will cut the compressor clutch if that temp drops below 3*C and put it back if grows above 4*C (if less cooling is required the limts are 10*C/off - 11*/on.) As long as the system is OK from all points of view those pressures set for the dual pressure switch will never be reached.

**Mclaren00** · 15th April 2017, 10:53 PM

Originally Posted by rick130

Ok, that's just plain dumb.

29psi in the high side is pumping air, there's no refrigerant left.

That HP cutout pressure is worse than scary, we set R404 cutouts lower. It's almost 410a territory.
The cutout pressure is 91*C !

Up in qld we set 404a at 380
And r134a at 230/250
Dunno if any different for car thou

**rick130** · 16th April 2017, 07:48 AM

Originally Posted by sierrafery

It's in the description of that dual pressure switch that it's there to protect the system from extremes of presures in case something goes wrong,

The high pressure cut out point is worse than extreme, no system running R134a should ever be allowed to reach those sort of cut out pressures.

91*C condensing temperature in refrigeration/air conditioning is insane. In a saturated environment (one where we have a liquid and vapour present together) there is a definite pressure/temperature relationship.
A pressure of 464psi with R134a=91*C (sorry for the mixed units)

To give you an idea of what I mean, in commercial refrigeration using R134a we set the HP cutout to around 200-220psi/1400-1540kpa gauge.
That's a safety limit, not working pressures.

Unfortunately 190-200psi is a normal working pressure in car/bus/truck/tractor a/c here, so the HP cut out is set higher, and I'm pulling numbers out of my arse here, but I wouldn't go higher than 260psi gauge, but IIRC most car systems were set to around 290-300psi. 260psi gauge is 65*C condensing pressure. That's considered extreme temps/pressures with that refrigerant.
That's where industry pressure/temperature charts max out. They don't go any higher.

464psi gauge pressure is bonkers, it's equal to 91* condensing pressure. The temperature at the discharge valves where the refrigerant is a superheated vapour, not a saturated vapour, it will be considerably higher, I'm guessing in excess of 50* higher, maybe more.

Refrigeration/air conditioning systems aren't designed for those temps, 65* saturated temps are considered extreme and the point where components start to fail.
I'm agog that Land Rover would use an HP limit so high.

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